Generally, an ultrasonic diagnostic apparatus is for performing a diagnosis such that ultrasonic waves are transmitted into a body of a test object from an ultrasonic probe (hereinafter, simply referred to as a probe), a reflected echo signal of the ultrasonic waves which have been reflected from the inside of the body is received by the probe, and an image or the like which is suitable for the test of a tissue, a function, or the like inside the body is created based on the received reflected echo signal (RF signal).
In such an ultrasonic diagnostic apparatus, for the test by a B mode image, it is preferable to obtain an image with a high image quality by placing the probe on the test body with a relatively strong force, pressing and deforming the body tissue so that the deep tissue can be closer to the probe, and imaging the tissue since the ultrasonic waves attenuate in the course of the propagation inside the body tissue.
On the other hand, in the bloodstream test such as the Doppler measurement or the CFM, since it is not possible to obtain correct information on the bloodstream because the cross-section of the blood vessel is deformed when the probe is placed on and pressed against the body tissue with an excessively strong force, it is preferable to perform the test with the pressurizing state which is gentler than that at the time of the B mode diagnosis.
In addition, since the body tissue has a nonlinearity in which the hardness of the tissue changes in accordance with the strength of the pressurizing even in the test by elastography for creating an image of elasticity information regarding the hardness or the softness of the body tissue, it is important to perform a diagnosis based on an elasticity image obtained under a pressurizing state with a constant pressure.
That is, although it has been recognized that a suitable pressurizing state (pressure) is different depending on the testing method, it is required that more experiences are accumulated until suitable pressurizing states are learned for all kinds of diagnoses. In addition, depending on a test, for example, a testing process frequently occurs in which a tomographic image of a site of interest is imaged and stored in the B mode and the B mode is then directly shifted to the Doppler measurement for obtaining the bloodstream information of the same cross-section. In the case of such a testing process, there is a concern that correct information on the bloodstream cannot be obtained as described above if a Doppler image is obtained while a relatively strong pressurizing state suitable for obtaining the B mode image is being maintained. That is, there is a concern that a test is performed while an unsuitable pressurizing state is being maintained in the respective testing methods or at the time of transferring between testing methods, which hinders a prompt appropriate diagnosis.
Accordingly, a method of measuring an actual pressure to be applied to the body tissue of the test object, that is, an absolute pressure to be applied to the body tissue (hereinafter, simply referred to as an absolute pressure) is disclosed in Patent Literature 1, for example. According to this method, an elastic coupler which is a deformable unit for the pressure measurement is attached to an ultrasonic wave transmitter/receiver surface of a probe, a pressure is applied to a test body by the probe via the elastic coupler, and an absolute pressure is obtained based on the deformation of the elastic coupler at that time.
Thus, according to the method of evaluating the pressurizing state disclosed in Patent Literature 1, it is possible to obtain the elasticity information on the hardness or softness of the body tissue by measuring absolute pressure applied to the test body, for example.